1. Field of the Invention
The present invention relates to a hydrogen storage matter for efficiently storing hydrogen used as a source material in fuel cells and a manufacturing method and manufacturing apparatus for the same; a hydrogen generating method; a hydrogen storage matter precursor used for a hydrogen storage matter and a manufacturing method for the same; a hydrogen storage matter packing container for packing a hydrogen storage matter therein and a movable body equipped with the same; and a gas refining apparatus used for hydrogen charge and discharge to and from a hydrogen storage matter.
2. Description of the Related Art
Fuel cells have been actively developed and some of them are already in practical use, as a clean energy source which does not emit a harmful substance, such as NOX or SOX, or a greenhouse effect gas, such as CO2. One of the important techniques to back up the fuel cell technology is a technique for storing hydrogen used as a source material in fuel cells. Various techniques for storing hydrogen have also been proposed, such as compression storage utilizing high-pressure cylinders and cooling storage utilizing liquid hydrogen.
However, in the case of hydrogen storage utilizing high-pressure cylinders, the hydrogen pressure is required to be higher to increase the hydrogen storage amount. In this case, the containers need to have a large weight, and the valves and so forth may cause problems in withstand pressure and reliability. On the other hand, as one of the methods for storing hydrogen as liquid, insulated containers are used for storing liquid hydrogen. In this case, since liquid hydrogen has a very low boiling point, it is necessary to use a large energy to liquefy hydrogen. Further, it is said that, when liquid hydrogen is supplied into insulated containers, hydrogen vaporizes and causes a loss of 10 to 20% in general, and a loss of 8% even with thermal insulation, which is economically unfavorable.
In order to solve the problems described above, attention is focused on a hydrogen storage technique utilizing hydrogen storage substances, which is advantageous in dispersion storage and transportation. As disclosed in R&D News Kansai 2002.7, pages 38-40, known as hydrogen storage substances are metal materials of, e.g., the rare earth family, titanium family, vanadium family, and magnesium family; light-weight element inorganic compound family materials, such as alanates (e.g., NaAlH4), utilizing a reversible disproportionation reaction; and carbon family materials, such as carbon nanotubes, activated charcoal. Of them, the light-weight element inorganic compound family materials and carbon family materials are promising as light-weight materials, wherein they are powder type materials.
In consideration of this, it is desired to develop an efficient storage technique utilizing such powder type light-weight materials: specifically, to develop a hydrogen storage matter with a high hydrogen storage rate per unit weight; a hydrogen storage matter with a high hydrogen storage rate per unit volume; a hydrogen storage matter showing hydrogen absorption and release performance within a low temperature range; and a hydrogen storage matter with good durability.
Further, it is necessary to provide designs suitable for respective hydrogen storage matters, concerning a mass production method and apparatus for manufacturing a powder type hydrogen storage matter; a method for efficiently preserving a hydrogen storage matter (specifically, a packing method to a predetermined container); a method of easily discharging hydrogen from a hydrogen storage matter packed in a predetermined container or the like; a method of efficiently charging hydrogen into a hydrogen storage matter precursor, which is a state of a hydrogen storage matter after hydrogen is discharged (or before hydrogen is charged); and a method of supplying a fuel cell with a fuel gas containing, as the main component, hydrogen discharged from a hydrogen storage matter.
Accordingly, at first, conventional powder type hydrogen storage matters will be discussed from the aspect of materials. As light-weight hydrogen storage matters, alanate family materials, such as NaAlH4 and LiAlH4, are well known and studied. Further, a hydrogen storage method using lithium nitride expressed by the following formula (1) is reported by Ruff, O. and Goerges, H., Berichte der Deutschen Chemischen Gesellschaft zu Berlin, Vol. 44, 502-6 (1911). Recently, the hydrogen storage method using lithium nitride expressed by the following formula (1) was restudied, as reported by Ping Chen et al., Interaction of hydrogen with metal nitrides and imides, NATURE Vol. 420, 21 Nov. 2002, pages 302-304.Li3N+2H2Li2NH+LiH+H2LiNH2+2LiH  (1)
As reported by these documents, where lithium nitride (Li3N) is used, it has been confirmed that hydrogen starts being absorbed from about 100° C., and hydrogen absorption reaches 9.3 mass % at 255° C. for 30 minutes. As regards the release characteristic of absorbed hydrogen, where heating is performed slowly at a low temperature-up rate, absorbed hydrogen changes through two level steps, such that it becomes 6.3 mass % at a temperature slightly lower than 200° C., and 3 mass % at a temperature of 320° C. or more.
In other words, this means that the reaction between lithium amide (LiNH2) and lithium hydride (LiH) starts at a temperature slightly lower than 200° C. This reaction is shown by the following formula (2) that corresponds to the right side of the formula (1). Further, the reaction between lithium imide (Li2NH) and LiH starts at a temperature of 320° C. or more. This reaction is shown by the following formula (3) that corresponds to the left side of the formula (1).LiNH2+2LiH→Li2NH+LiH+H2↑  (2)Li2NH+LiH→Li3N+H2↑  (3)
FIG. 1 is a view showing gas emission spectrum characteristic lines of desorption gas from an Li3N sample heated after it was charged with hydrogen at a hydrogen pressure of 3 MPa and 200° C. by the same method as disclosed in the documents described above. The sample was heated at a temperature-up rate of 5° C./minute. In FIG. 1, a characteristic line A denotes a hydrogen emission spectrum line, and a characteristic line B denotes an ammonia gas (NH3(g)) emission spectrum line. As shown in FIG. 1, the hydrogen release characteristic obtained by the conventional method rendered a wide temperature range of 200 to 400 ° C., and had a large peak on the high temperature side (near 320° C.).
The technique disclosed in the documents described above is an effective hydrogen storage method using lithium nitride, which is a light-weight metal compound. However, the effective hydrogen storage rate thereof is small within a low temperature range of around 200° C., and thus it is necessary to perform heating within a high temperature range of 320° C. or more in order to realize hydrogen charge and discharge with a high volume. Further, according to the technique disclosed in the documents described above, the temperature-up rate is set smaller as the temperature is closer to the hydrogen absorption and release peak temperatures. Consequently, the heating takes long time and thereby makes it difficult to obtain a high response, which is not practical.
Next, conventional techniques will be discussed in relation to a manufacturing method and manufacturing apparatus for a powder type hydrogen storage matter. For example, the present inventors have disclosed, in Jpn. Pat. Appln. KOKAI Publication No. 2001-302224, that nano-structured graphite can be formed by a mechanical crushing process within a hydrogen atmosphere. Because such fine crushing requires high energy, Jpn. Pat. Appln. KOKAI Publication No. 2001-302224 discloses use of a planetary ball mill that can perform mechanical crushing with high energy. This crushing method is applicable to lithium family materials, such as lithium nitride described above, and alanate family materials.
However, while the planetary ball mill can give high energy to a process object to be crushed, there is a limit of increase in size because it is of the gravity type, which is not suitable for mass production. Further, since the crushing process performed by the planetary ball mill is dry crushing, a problem arises such that, when the crushing proceeds and the process object is turned into fine particles, the particles are easily agglomerated and thereby hindering progress of crushing. Furthermore, when the hydrogen storage matter formed by the crushing process is transferred to another container, a hydrogen storage matter of a certain type requires this transfer to be performed in an inactive atmosphere to prevent contact with air or the like. In this case, it is not easy to handle the hydrogen storage matter formed by the crushing process.
If a hydrogen storage matter precursor is formed by a method other than a method using mechanical crushing to form a hydrogen storage matter, there is a chance of increasing the hydrogen storage rate. Accordingly, it is strongly demanded to develop a hydrogen storage matter precursor and a manufacturing method for the same, which can increase the hydrogen storage rate.
Next, conventional techniques will be discussed in relation to a method of preserving a hydrogen storage matter. In general, research and development have been made for hydrogen storage tanks that can store a large amount of hydrogen by a small volume, in place of hydrogen cylinders. Hydrogen storage alloys have been developed as hydrogen storage matters to be contained in hydrogen storage tanks of this kind. Hydrogen storage tanks using a hydrogen storage alloy are disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2000-120996, No. 2002-122294, No. 2002-221297, and No. 2002-340430.
However, hydrogen storage alloys show a low hydrogen storage rate per unit weight, and thus hydrogen storage tanks using a hydrogen storage alloy are not yet in practical use. On the other hand, light-weight powder type hydrogen storage matters, such as alanate family materials, carbon family materials, and lithium family materials, e.g., lithium nitride, show powder characteristics and hydrogen absorption and release characteristics different from those of conventional storage alloys. Accordingly, unless a packing container for packing such a material has a structure suitable for its characteristics, it is difficult to achieve a sufficient hydrogen storage amount per unit volume. However, packing containers for a light-weight powder type hydrogen storage matter of this kind have not yet been well developed.
Next, conventional techniques will be discussed in relation to supply of a fuel gas to a fuel cell. In the case of compression storage utilizing high-pressure cylinders and cooling storage utilizing liquid hydrogen, both conventionally used, there is a common problem such that, during hydrogen charge or discharge being handled, moisture mixes therein along with air, and may cause poisoning of a fuel cell when the moisture enters the fuel cell. In order to solve this problem, Jpn. Pat. Appln. KOKAI Publication No. 59-47599 discloses use of a removing agent, which is formed of an absorbent mixture of a metal hydride and a molecular sieve.
However, in the case of the lithium family material shown in the formula (1), when it is heated, NH3(g) may be generated along with hydrogen by decomposition or the like of LiNH2. If the hydrogen containing NH3(g) enters a fuel cell, it causes a problem about poisoning of the fuel cell. However, there is no refining apparatus proposed so far to remove impurities from such hydrogen containing NH3(g).